Transportation by water is an important aspect of modern commerce. Water-based transportation has been the largest carrier of freight throughout recorded history. Large vessels such as tankers and freight vessels are especially valuable since efficiency and seaworthiness increase with the size of the vessel. Water-based vessels are also used for passenger travel, such as passenger and car ferries, as well as cruises and other leisure travel.
Water-based vessels must carry, generate or otherwise harness all the power they consume during a trip away from land. Carbon-based liquid fuel is the principal power source for commercial water transportation. A single passenger ferry may burn million dollars of fuel each year. Although alternative power sources have been explored, the shipping industry is reliant on fuel. The environmental effect of burning fuel and the price of the fuel itself are substantial. Partially wind-powered cargo vessels have been proposed for reducing fuel consumption by fuel-burning vessels.
Rigid wing sails are an alternative to traditional fabric sails. A rigid wing sail acts as an airfoil to create lift in the desired direction. Although more efficient than a traditional fabric sail, a rigid wing sail typically adds more weight to a vessel. It is desirable to increase the efficiency of a rigid wing sail.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.